The invention relates to novel compositions and methods for enhancing permeation of topically administered drugs by incorporating therein pyroglutamic acid esters as dermal penetration enhancing agents.
Transdermal drug delivery to achieve systemic effect is an area of much current interest and activity. While the cutaneous route of input is advantageous in many respects such as ease of use, better patient compliance, decreased first pass metabolism etc., the excellent barrier nature of the skin has so far limited the drugs considered suitable for transdermal delivery to very few. The use of adjunctive chemicals known as skin penetration enhancers widens the scope of transdermal drug delivery. Such use involves controlled impairment of the skin's protective layer, the stratum corneum. Ideally, no elements of the skin other than this horny layer should be involved in such a drug delivery approach, because participation of any living tissue could result in cellular insult and lead to an irritant or allergic response. So an ideal penetration enhancer is one which speeds the permeation of the drug through the stratum corneum, without itself crossing this barrier, or if it crosses, undergoes fast metabolic destruction and/or detoxification in the viable area of the skin. This invention deals with an analagous series of penetration enhancers of the latter type.
It is well known that a number of therapeutically active agents, such as .beta.-blockers, antihypertensives, antiarrhythmics, antianginal agents, vasodilators, antiemetics, antibacterials, antifungals, corticosteroids, antiinflammatories and the like when administered to warm-blooded animals by a number of various routes such as by intravenous infusion, intramuscular injection, oral, rectal or buccal routes, enter the general circulation and produce the appropriate systemic therapeutic effect. It is also known that the aforementioned methods of administration have certain disadvantages. For example, the intravenous and intramuscular routes are not only painful for the patient, but also must be performed by a trained individual. Buccal and rectal administration often produce discomfort and annoyances for the patient. Oral administration, although generally acceptable for the patient, often does not deliver much of the therapeutic agent to systemic circulation. This diminished drug delivery is usually attributed to poor absorption from the gastrointestinal tract and/or to degradation of the agent by the acidic medium of the stomach, by the enzymes in the gastrointestinal tract and surrounding tissue, or by the rapid metabolism by enzymes of the liver through which the drug must pass before it enters the systemic circulation. For example, drugs such as anti-bacterials, narcotic analgesics, .beta.-blockers and others require relatively high doses when given orally due to the remarkable liver metabolism encountered. Effective delivery of such drugs through the skin would require much lower doses because the so-called "first pass" metabolism would be avoided. Additionally, the topical application of the drug has the advantage that their pharmacological action is exhibited gradually over an extended period of time avoiding the possibility of inducing undesirable physiological action by abrupt increase in concentration in vivo.
But most drugs are not absorbed in sufficient concentration through the skin to exhibit pharmacological effect. This is because skin is an effective barrier to penetration. The outer layer of the epidermis, called the stratum corneum, offers the maximum resistance to penetration, whereas the lowerlayers are relatively permeable. For proper treatment of dermal conditions, it is important that the active agent penetrate the stratum corneum where it is retained. From this reservoir in the outer layer, the therapeutic agent could be slowly released and penetrates the underlying areas where it could exhibit its therapeutic or cosmetic effect. When dermatological agents such as sunscreens, which protect the underlying tissue from external factors (ultraviolet rays) are used, maximum retention in the stratum corneum is essential. On the other hand, the relative permeability of the layers of the epidermis below the stratum corneum can also allow access to the systemic circulation; indeed, it is necessary for the therapeutic agent to penetrate the stratum corneum in order to provide systemic therapeutic effect from the transdermal route.